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Gray Wastewater Treatment Chemicals

Gray water includes all source of household wastewater except toilets. High water demand, low rainfall and economic concerns in many parts of the world have raised interest in gray water treatment and recycling. Gray water contains an extensive list of contaminants, including microbes that carry risk of infection. Microbial contaminants in recycled gray water are generally treated by chemical disinfection.

  1. Microbes

    • Microbes identified in gray water include bacteria, viruses, protozoa and helminthes. Microbes are released into graywater via fecal contamination, either through hand washing after toilet use or baby diapers. Washing raw meat is also a source of contamination. Microbes in recycled gray water pose an infection risk, especially in immune-compromised individuals such as the elderly, HIV patients and organ transplant recipients. It is also possible for microbe-contaminated gray water for irrigation purposes to pollute groundwater sources and affect drinking water.

    Chlorine

    • Chlorine is the most commonly used disinfection chemical, and is applied to a range of water treatments including drinking water and swimming pools. Approximately 15 mg of chlorine is used per liter of gray water. Chlorine is inexpensive and available in granules, tablets and in household bleach. Large organic pollutants shield some bacteria from chlorine disinfection. This is prevented by filtering gray water to remove its organic content.

    Ferrate (VI) Salts

    • Ferrate (VI) salts such as sodium ferrate and potassium ferrate are strong oxidizing agents and coagulants used in gray water treatment. Its properties allow it to disinfect microbes, remove suspended particles and degrade organic and inorganic pollutants. Despite this, ferrate (VI) treatment is not applied on a large scale due to its instability, low yield during preparation and lack of research into its effectiveness over other chemical treatments.

    Essential Oils

    • There are several essential oils with antimicrobial properties. Researchers from Cranfield University in the UK demonstrated that origanum oil and carvacrol are effective at disinfection. Coliform bacteria were reduced to undetectable levels in 100 ml of water treated with 468 mg per liter of origanum oil. Essential oil treatment faces similar problems as chlorine and ferrate (VI) salts, regarding the organic content of gray water blocking disinfection, and an insufficient amount of oil produced for large-scale application.

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